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<title>Predominance Area Diagrams</title>
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<p>A <b>predominance area diagram</b> shows the species formed with a given
<nobr>&#147;main&#148;</nobr> component as a function of two variables.
The following rules are used:</p>
<ul>
<li>A solid is always shown on top of aqueous species, even when the solid
	has a very small concentration,</li>
<li>If more than one solid are formed, the solid with the largest fraction
	of the main component is shown,</li>
<li>If no solid is formed, the diagram shows the aqueous species which has the
	largest fraction of the main component.</li>
</ul>

<p>A special type of predominance area diagram is the potential-pH diagram,
also called a <i>Pourbaix</i> diagram. The following figure shows a
potential-pH diagram <nobr>for iron:</nobr></p>

<p>
<center><img src="images/Diagr_Pred.gif" border="1" width="362" height="259" alt="Eh-pH diagram"></center>
</p>

<p>This diagram was obtained with the following input file:</p>
<pre><code> 3, 13, 7, 0
H+, e-, Fe 2+
Fe 3+     ,-13.02   0 -1 1, Fe(OH)2   ,-20.8   -2  0 1
Fe(OH)3-  ,-33.4   -3  0 1, Fe(OH)4 2-,-46.35  -4  0 1
FeOH+     ,-10.2   -1  0 1, OH-       ,-14.0   -1  0 0
Fe(OH)2+  ,-18.69  -2 -1 1, Fe(OH)3   ,-25.58  -3 -1 1
Fe(OH)4-  ,-34.62  -4 -1 1, Fe2(OH)2+4,-28.99  -2 -2 2
Fe3(OH)4+5,-45.36  -4 -3 3, FeO4 2-   ,-125.87 -8 -4 1
FeOH 2+   ,-15.21  -1 -1 1,
Fe(c)     ,-16.097  0  2 1, Fe(OH)2(c), -12.996 -2  0 1
Fe3O4(c)  ,-37.077 -8 -2 3, Fe(OH)3(am),-17.911 -3 -1 1
Fe2O3(cr) ,-26.448 -6 -2 2, Fe3(OH)8(c),-46.262 -8 -2 3
FeOOH(cr) ,-14.02  -3 -1 1
EH, e-, H+, Fe 2+,
LAV, 0 -13,  LAV, 16.9034 -18.5937, T, 1E-5</code></pre>
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